Isokinetic torques and kicking maximal ball velocity in young soccer players.

The purpose of this study is to assess if there is any correlation between isokinetic testing and field performance of young soccer players. The isokinetic peak torques of the knee extensor muscles in sitting position (TKE), and those of the hip flexor muscles in standing position (THF) were measured in 24 junior soccer players. Four angular velocities (omega = 1.05, 3.14, 4.19, 5.23 rad.s-1 or 60, 180, 240, 300 deg.s-1) were used for the knee extensors and three (1.05, 3.14, 4.19 rad.s-1) for the hip flexors. On the field the subjects were asked to kick a stationary soccer ball as fast as possible against a barrier and the mean linear velocity over a 10 m path (v) was measured. TKE of the non dominant limb were higher than those of the opposite one at the three highest omega (p < 0.05). On the contrary the THF of the dominant limbs were higher than those of the controlateral, at the two highest omega. When the ball was kicked by the dominant or non dominant limbs, the mean values and standard deviations (+/- SD) of v were 23.6 (+/- 2.5) and 21.4 (+/- 2.6) m.s-1. Torques and v were always positively correlated to each other; however, only in few cases was this relationship statistically significant. In conclusion the isokinetic torques do not seem to be good predictors of v, one of the several factors which determine the global performances of the soccer players.

Physiological responses during prolonged exercise at the power output corresponding to the blood lactate threshold.

Heart rate (HR) and oxygen uptake (VO2) at the mechanical power (W) corresponding to the capillary blood lactate ([la]cap) of 4 mmol.l-1 (Wlt) were measured in 34 healthy male subjects during incremental exercise (Winc). On the basis of these measurements, the subjects were asked to cycle at Wlt for 60 min (steady-state exercise, Wss). Twenty subjects could not reach the target time (mean exhaustion time, te, 38.2 min, SD 5.3), while 6 of the 14 remaining subjects declared themselves exhausted at the end of exercise. The final [la]cap if the two groups of exhausted subjects were 5.3 mmol.l-1, SD 2.3 and 4.3 mmol.l-1, SD 1.1, respectively. At the end of Wss, [la]cap and HR were significantly lower in the 8 unexhausted subjects than in the other subjects. This group also had a lower HR at Wlt during Winc. The HR and VO2 appeared to be higher during Wss than during Winc. When all subjects were ranked according to their te during Wss, Wlt (expressed per kilogram of body mass) was found to be negatively related to te. In conclusion, during Winc, measurements of physiological variables at fixed [la]cap give a poor prediction of their trends during Wss and of the relative te; at the same work load [la]cap can be quite different in the two experimental conditions. Furthermore, resistance to exercise fatigue at Wlt seems lower in the fitter subjects.